Temperature stress in combination with increased pCO2 lead to increased deformities in European lobster juveniles (Homarus gammarus), but what happens in the exoskeleton and gastroliths?

Chair: Elvira Poloczanska

A-L. Agnalt, E.S. Grefsrud, E. Farestveit, I. Fiksdal, M. Larsen, G. Thorsheim

Institute of Marine Research, PoBox 1870Nordnes, 5817 Bergen, Norway

Background
It has been shown that European lobster ( Homarus gammarus) juveniles exposed to increased pCO2 develop deformities (Agnalt et al. 2014). We wanted to assess if increased temperature could further stress the juveniles. We have also focused on element analysis, examination of exoskeleton and gastroliths (calcium storage) development to elucidate the causes of the deformities.

Methods
Juveniles were exposed to 14, 18 and 22ºC under ambient, 1000 and 1400 µatm pCO2. Mortality, growth and deformities were monitored. All surviving juveniles were x-rayed for gastrolith detection. A selection of juveniles were analysed for Ca, Mg, Fe, Al, Si content. The exoskeleton was investigated with scanning electronic microscope (SEM). Parallel, a separate study focused on the development of the exoskeleton (SEM) and gastrolith (x-ray) during one moulting cycle under control conditions (ph=8.1).

Findings
After nine weeks of exposure, 30% of the juveniles raised in 14ºC and exposed to high pCO2 had developed deformities. At 18ºC and 20ºC the corresponding deformities were 60% and 80% respectively. Mortality increased with increasing temperature, but with no consistent pattern with pCO2 exposure. The content of Ca varied from 12-306 g/kg, Mg from 0.7-21 g/kg and Ca/Mg ratio 0.9-112. The Ca/MG ratio in gastroliths varied from 45-112. The exoskeleton also contains aluminium, 3.02-106 mg/kg, predominantly found in the epicuticle. In a moulting cycle of 30 days the gastroliths starts developing about day 17. Gastrolith is maximum in size hours before moulting, falls into the stomach and dissolves. Development of the new exoskeleton during the moulting cycle is described and compared with OA exposed juveniles.

Conclusions
Increased temperature in combination with CO 2-exposure will lead to increased deformities in juvenile European lobster. To understand how deformities is being developed a thorough understanding of processes taking place during the moulting cycle is needed.